Spumavirus, also known as foamy virus for the characteristics of vacuolization the virus induces in cell culture, belongs to a distinct group of retroviruses. The simian foamy viruses (SFVs) include isolates from Old World and New World monkeys and are classified into 10 different serotypes based on serological cross-reactivities. Virus appears to persist in the host for a long period of time in a latent form and can exist in the presence of neutralizing antibody.
Currently the most studied retrovirus, Human Immunodeficiency Virus, is believed to be derived from nonhuman primate transmission into humans at some past time. Concerns about the risk of transmission of retroviruses from non-human primates to humans working in research laboratories were heightened in the early 1990's when two persons developed antibodies to SIV (Simian Immunodeficiency Virus) following work- related exposures, one of whom had clear evidence of persistent viral infection. (See CDC. Anonymous survey for simian immunodeficiency virus (SIV) seropositivity in SIV laboratory researchers--United States, 1992. MMWR Morb Mort Wkly Rep 1992; 41: 814-5; Khabbaz R. F., et al. Brief report: infection of a laboratory worker with simian immunodeficiency virus. New Eng J. Med. 1994; 330: 172-7; Khabbaz R. F., et al. Simian immunodeficiency virus needlestick accident in a laboratory worker. Lancet 1992; 340: 271-3; and CDC. Guideline to prevent simian immunodeficiency virus infection in laboratory workers and animal handlers. MMWR 1988; 37: 693-704.) In addition to SIV, nonhuman primate species used in biomedical research are commonly infected with SFV (simian foamy virus), STLV (simian t-cell lymphotrophic virus), and/or type D retroviruses. All of these retroviruses cause lifelong infections in nonhuman primates, and some are known to be transmissible through sexual contact, blood, or breast feeding. Natural SFV infections in non-human primates have not been definitively associated with disease. In non-human primates, infection with the other retroviruses may result in a clinical spectrum ranging from asymptomatic infection to life threatening immunodeficiency syndromes or lymphoproliferative disorders. The transmission routes of SFVs among non-human primates remain undefined, but the prevalence of seroreactivity is high among captive adult non-human primates.
Studies of the prevalence of spumavirus infection of humans are limited and the findings are not definitive. Though there is some evidence of human infection with SFV (antibodies and positive PCR results), such occurrence has been reported in only two persons, both of whom had occupational risks for infection. Associated disease was not reported in either. (See Schweizer M., et al. Absence of foamy virus DNA in Graves' disease. AIDS Res & Human Retrov 1994; 10: 601-5; Neumann-Haefelin D., et al., Foamy viruses. Intervirology 1993; 35: 196-207; and Schweizer M., et al., Markers of foamy virus infections in monkeys, apes, and accidentally infected humans: appropriate testing fails to confirm suspected foamy virus prevalence in humans. AIDS Res & Human Retrov 1995; 11: 161-70.) There have been no published reports that virus was ever isolated from these infected individuals.
Other inconclusive evidence was seen in early studies which described a relatively high rate of seroreactivity to antibodies to spumaviruses among human populations not known to be exposed to non-human primates. In some instances seroreactivity was suggestively linked to human disease, including disorders of the central nervous system, thyroid disease, and Chronic Fatigue Syndrome. In most instances these studies lacked definitive evidence of human infection and were not subsequently confirmed. (See Heneine W., et al., Absence of evidence for human spumaretrovirus sequences in patients with Graves' disease letter!. J Acq Immune Defic Synd & Human Retrov. 1995; 9: 99-101; Simonsen L., et al.,. Absence of evidence for infection with the human spuma retrovirus in an outbreak of Meniere-like vertiginous illness in Wyoming, USA letter!. Acta Oto-Laryngologica 1994; 114: 223-4; and Heneine W., et al., Lack of evidence for infection with known human and animal retroviruses in patients with chronic fatigue syndrome. Clin Infect Dis 1994; 18: S121-5).
To the knowledge of the inventors, there has not been a documented, definitive isolation of a nonhuman primate origin spumavirus from humans. Previous reports of human spumavirus isolates are now widely regarded as laboratory contaminants.
Recent publications indicate that earlier serological tests showing human spumavirus antibodies in the human population were incorrect. Immunological investigation of a previously reported human spumavirus revealed that it shared common antigens in complement fixation, immunofluorescence and neutralization assays with the chimpanzee foamy virus, SFV-6. Furthermore, failure to detect serological evidence of HFV infection in people from a wide geographical area suggested that this virus isolate was a variant of SFV-6, particularly since sera from chimpanzees naturally infected with SFV-6 neutralized both viruses. In a survey for prevalence of human foamy virus in more than 5000 human sera, collected from geographically diverse populations, none of the serum samples were confirmed as positive. Taken together with sequence analysis endorsing the phylogenetic closeness of the purported human spumavirus to SFV-6/7, these data strongly suggest that human foamy virus is not naturally found in the human population. (See Ali, M. et al., "No Evidence of Antibody to Human Foamy Virus in Widespread Human Populations," AIDS Research and Human Retroviruses, Vol. 12, No. 15, 1996.)
Recent concern that xenotransplantation, the use of living tissues from nonhuman species in humans for medical purposes, may introduce new infections into the human community has increased the importance of defining the ability of simian retroviruses to infect and/or cause disease in humans (See Chapman L. E., et al. Xenotransplantation and xenogeneic infections. New Engl J Med 1995; 333: 1498-1501; DHHS. Docket No. 96M-0311. Draft Public Health Service (PHS) Guideline on Infectious Disease Issues in Xenotransplantation. Federal Register Vol.61, No. 185. Sep. 23, 1996.). The primary animal species considered as donors for xenografts are baboons and pigs. Thus, what is needed are compositions and methods for detecting viruses that may be transmitted from the nonhuman organ donors to the recipient human. Additionally, information regarding these transmissible agents may provide valuable information about the organ donors' cellular receptors that may be important for transplantation success.
Gene therapies have long looked for a good vector that can transport the foreign gene of choice into human cells. The lack of any known disease associated with the virus of the present invention makes the present invention an ideal candidate for gene therapy regimens. Thus, compositions and methods for gene therapy are needed that use a vector capable of carrying a significant amount of foreign DNA that will enter the host organism and not cause disease.